RF communication systems in many varied forms are well understood in the art. For example, wide area low bandwidth systems (such as paging systems) typically provide one way communications on relatively narrow channels at relatively low bit rates (such as 1200 bps). Medium area systems, such as SMR trunking, provide more functionality over a more limited geographic area and rely in part upon a higher bit rate (such as 3600 bps) to support necessary data communications. Limited coverage high bandwidth systems are also known, and typically require the use of much higher bandwidth channels (such as 200 kHz to 2 MHz) and much higher bit rates (such as 270 kbps to 1.6 mbps). Examples of such systems are digital cellular communications systems as envisioned pursuant to the GSM program, and the digital electronic cordless telephone (DECT) program intended for on-site applications.
As is known in the art, these systems are collectively similar in that each communication supported by these communication systems necessarily includes an RF wireless communication link.
These and other systems are, or will soon be, found in numerous locations throughout the world, and often in overlapping configurations. That is to say, in a given metropolitan area, a particular communication user may have theoretical access to a plurality of communication systems. Since these communication systems tend to have differing operating characteristics, however, such as differing bit rates, bandwidths, signalling protocols, registration requirements and the like, in practice a single user will only be able to access such multiple systems by obtaining multiple communication units that are each compatible with one of the systems. For example, to obtain benefit of only some of the RF services available in his area, a user may equip his automobile with a mobile cellular telephone, one or more land mobile radios (to allow access to one or more trunked or conventional land mobile systems), and a mobile data terminal to allow exchange of data. In addition, the user may himself carry a pager.
The necessity of obtaining, maintaining, and operating all of this equipment to gain access to only a few of the RF communication services offered in a particular area is undesirable. A need exists for a communication unit that can readily access more than one type of communication system, and for an infrastructure that will accommodate such a communication unit to afford access to the differing communication systems.